Athenian character penned by dramatist — I'm one (5)
I believe the answer is:
timon
'athenian character' is the definition.
(Timon of Athens)
'penned by dramatist i'm one' is the wordplay.
'penned by' says the answer is hidden in the clue.
'TIMON' is hidden in the letters of 'dramatist im one'.
(Other definitions for timon that I've seen before include "part of Shakespeare" , "lead in Greek tragedy?" , "The Bard's Athenian" , "title role" , "- - of Athens (Shakespeare)" .)